The invention relates to improvements in apparatus for manipulating commodities in gathering machines for paper sheets and the like. More particularly, the invention relates to improvements in apparatus which can be used to monitor condition and/or the presence or absence of sheets in certain sections of machines or production lines which are used for bookbinding, for accumulation of sheets into pamphlets or brochures, and for similar purposes.
It is known to monitor successive sheets which are drawn from a magazine and are transferred onto a sword or onto another part of a gathering machine wherein the sheets (e.g., signatures) are accumulated into larger groups preparatory to sewing, stapling or another mode of connecting the assembled sheets or groups of sheets to each other. As a rule, the apparatus are provided with means for monitoring the thickness of sheets which are engaged by the gripper or grippers on the conveyor which serves to draw successive sheets from a magazine or from another suitable source. The density monitoring device normally includes a roller or a like part which rides over the sheet or sheets advancing from the magazine to the next station. The extent of displacement of the roller from its normal or anticipated position is indicative of the presence or absence of a sheet or of the presence of two or more sheets or groups of sheets in lieu of one. Signals which are generated in response to movement of the roller from its normal or anticipated position are used to arrest the conveyor or the entire machine in which the conveyor is in use.
The just described monitoring apparatus operates satisfactorily as long as the speed of the conveyor for the gripper or grippers remains below a certain maximum permissible value. If the speed is increased, the roller must be biased against the conveyor and the sheet or sheets thereon with a very large force so that the roller is likely to deface and/or otherwise damage the sheets. Another drawback of such monitoring apparatus is that the cost of properly mounting the roller with reference to the gripper or grippers and vice versa is very high because the mounting must be such that the gripper or grippers and the roller cannot perform any stray movements (such as vibratory movements) relative to each other. Stray movements would distort the signals which are generated as a result of monitoring of the position of the roller with reference to the conveyor for the gripper or grippers.